1. Field of the Invention
This invention relates generally to an industrial truck having a forward propulsion unit for horizontal movement of the industrial truck, a driver""s platform that can be raised or lowered by means of a vertical propulsion unit, at least one control device to control the vertical propulsion unit and the forward propulsion unit, and a blocking device that can be adjusted as desired to block or allow access to the driver""s platform. The invention also relates to a method for the operation of an industrial truck having a forward propulsion unit for horizontal movement of the industrial truck, a driver""s platform that can be raised or lowered by means of a vertical propulsion unit, at least one control device to control the vertical propulsion unit and the forward propulsion unit, and a blocking device that can be adjusted as desired to block or allow access to the driver""s platform in which a first signal transmitter is effectively connected with the control device, the output signal of which first signal transmitter changes as a function of a position of the driver""s platform below or above a specified elevation, and in which a second signal transmitter is effectively connected with the control device, the output signal of which second signal transmitter changes as a function of the position of the blocking device.
2. Description of the Currently Available Technology
Industrial trucks with an elevatable driver""s platform are typically equipped with a blocking device by means of which the access to the driver""s platform can be blocked. Such a blocking device is generally required on all industrial trucks on which the driver""s platform can be raised above a specified elevation, such as about 1.2 meters. The blocking device is frequently embodied as a gate that can be moved manually by the driver. A signal transmitter located on or near the gate determines the position of the gate and generates a signal that indicates whether the gate is open or closed. Industrial trucks may also be equipped with a signal transmitter for elevation that indicates whether the driver""s platform is elevated above the specified height.
To maintain compliance with occupational safety regulations, it is conventional to connect the signal transmitters for elevation and the status of the blocking device with an emergency off function of the industrial truck. The forward propulsion unit and the vertical propulsion unit are automatically deactivated if the driver""s platform has been elevated at least to the specified height and the blocking device is simultaneously open. This conventional device frequently results in an unintentional deactivation or shutdown of the industrial truck, in particular if, during an elevation of the driver""s platform, the specified height is reached while the gate is open.
An object of the invention is therefore to provide an industrial truck of the type described above as well as a method for the operation of the industrial truck in which, while complying with conventional safety requirements, an unintentional shutdown of the entire industrial truck can be prevented.
To accomplish this object, the invention teaches that an industrial truck control device is designed so that, as a function of the elevation of the driver""s platform and the position of the blocking device, either all the functions of the forward propulsion unit and of the vertical propulsion unit are enabled; or all the functions of the forward propulsion unit and of the vertical propulsion unit are disabled; or an elevation of the driver""s platform is disabled, although the driver""s platform can be lowered and/or the industrial truck can be moved horizontally. Depending on the operating status of the industrial truck, therefore, certain functions of the industrial truck are disabled by the control device if the driver""s platform has been elevated above the specified height.
For this purpose, it is particularly advantageous if the control device is designed so that if the blocking device is open during the elevation of the driver""s platform, as soon as a specified height is reached, any further elevation of the driver""s platform is prevented, although the driver""s platform can still be lowered and/or the industrial truck can be moved horizontally, e.g., driven normally. The control device makes it impossible to elevate the driver""s platform beyond the specified height while the blocking device is open. When this specified elevation is reached, however, the industrial truck can still be driven normally and the driver""s platform can be lowered.
The control device is further designed so that, after an opening of the blocking device, if the driver""s platform is above the specified elevation, any vertical movement of the driver""s platform as well as a horizontal movement, e.g., forward or reverse movement, of the industrial truck is prevented. The vertical propulsion unit and the forward propulsion unit are therefore kept completely stationary as long as the driver""s platform is above the specified level and the blocking device is opened.
The invention teaches that it is appropriate if there is a first signal transmitter that is effectively, e.g., operationally, connected with the control device, whereby the output signal from the first signal transmitter changes as a function of a position of the driver""s platform above or below the specified elevation. A first signal transmitter that has two switched positions for the output signal can be used.
There is preferably also a second signal transmitter that is effectively, e.g., operationally, connected with the control device, whereby the output signal of this second signal transmitter changes as a function of the position of the blocking device. Here again, a signal transmitter that has two switched positions for the output signal can be used, whereby the second signal transmitter assumes a first switched position when the blocking device is in the open position and a second switched position when the blocking device is in the closed position.
It is particularly advantageous if the control device is designed so that if the output signal of one of the two signal transmitters is switched over, the control device automatically verifies the control signal of the other signal transmitter. If the control device records the switchover of one of the two signal transmitters, there is an automatic verification of the status of the other signal transmitter. Depending on the output signals of the two signal transmitters, the functions of the forward propulsion unit and some or all of the functions of the vertical propulsion unit are enabled or disabled.
With regard to the method, the invention teaches that after a switchover of the output signal of one of the two signal transmitters, the control device automatically performs a verification of the control signal of the other signal transmitter, and then either enables all the functions of the forward propulsion unit and of the vertical propulsion unit; or disables all the functions of the forward propulsion unit and of the vertical propulsion unit; or an elevation of the driver""s platform is disabled, although the driver""s platform can be lowered and/or the industrial truck can be moved horizontally, i.e., driven forward or backward.